ソース見てみるよー

defrequire_dependency(file_name, message = "No such file to load -- %s")
file_name = file_name.to_path if file_name.respond_to?(:to_path)
unless file_name.is_a?(String)
raiseArgumentError, "the file name must either be a String or implement #to_path -- you passed #{file_name.inspect}"endDependencies.depend_on(file_name, message)
end